Vancouver’s VanDusen Botanical Gardens was redesigned and completed in 2011, making a strong impact on environmentally conscious building practices. For the new visitor center, designers wanted to reduce the facility’s carbon footprint by creating a structure designed to LEED Platinum certification standards and to meet the The Living Building Challenge.

The visitor’s center featured a unique, curved rammed earth wall in the shape of an orchid. The VanDusen project team enlisted Torrent Shotcrete Structures to create a structural wall to reinforce the oscillating rammed-earth wall, which would require waterproofing. As the building needed to align with strict LEED Platinum requirements, the shotcrete wall’s waterproofing system had to conform to strict environmental specifications, and work as a long-term solution.

Structural shotcrete saves time and money, and requires one-half the forming and equipment of regular cast-in-place methods, while also allowing for considerable design flexibility.

Waterproofing shotcrete can be challenging. Shotcrete has the potential to be more permeable and have larger, more frequent voids in the hands of an inexperienced contractor.

Surface-applied waterproofing systems

Surface-applied systems include coatings and sheet membranes and can be either polymer- or bitumen-based.

  • Surface coatings

Although surface coatings work well on projects with multiple plane transitions, intricate geometric shapes, and protrusions, the polymer (or liquid) coatings can deteriorate when exposed to ultraviolet radiation and cannot withstand foot traffic. The liquids themselves also contain toxic and hazardous volatile organic compounds (VOCs).

  • Sheet membranes

Sheet membranes are flexible sheets adhered to the wall and sealed at the seams. This method has excellent crack-bridging ability but has similar limitations to coatings.

Neither method of surface-applied waterproofing was appropriate for the VanDusen centre’s design. Surface preparation installing a coating or membrane would have taken up valuable time. More importantly, the surface barrier would likely have been damaged while installing the rammed-earth portion of wall, rendering the waterproofing useless. Using VOCs in liquid-applied membranes, as well as the primers and joint adhesives for sheet membranes, also made these systems incompatible with the project’s environmental requirements.

Integral systems

Integral systems are admixtures added at the batching plant and delivered pre-mixed into the concrete. Instead of forming a barrier on the concrete’s surface, they turn the full-depth of the concrete itself into a water barrier. They do not require additional surface preparation or labor to install, and once installed, they cannot be damaged by scratches and punctures.

  • Reactive/crystalline systems

When added to the concrete mix, crystalline system chemicals grow millions of needle-like crystals throughout the concrete matrix, blocking the movement of water in all directions. These crystals then remain dormant until cracks form, when they react with any incoming water to “self-seal” the crack and maintain a watertight barrier.

Waterproofing solution

After being presented with various waterproofing options, a crystalline system—Krystol Internal Membrane (KIM)— was specified. As the benchmark PRAH (Permeability Reducing Admixture – Hydrostatic Conditions), KIM can withstand extreme hydrostatic pressure and can be used in conjunction with a compatible crystalline waterstop system that can withstand the rigorous shotcrete process.

The building successfully achieved its goal of being self-sufficient and carbon-neutral, along with LEED Platinum certification and is on its way to becoming the first Living Building Challenge fully certified structure in Canada.

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